Various techniques have been proposed to capture an image of the surrounding of a vehicle using a vehicle-mounted camera and recognize objects (such as vehicles and pedestrians) and road markings and signs (paint on a road surface such as dividing lines and signs such as stop) in the captured image. For example, if a dividing line as paint on a road can be recognized using a vehicle-mounted camera and a vehicle position in a lane can be found, then warning can be issued to a driver when the vehicle departs from the lane or a steering and a brake can be controlled to suppress the departure.
As such a system issuing warning when a vehicle departs from a lane, lane departure warning systems (LDWS) specified by JIS D 0804 of JIS (Japanese Industrial Standard) are available. In order to implement this standard using a vehicle-mounted camera configured to capture an image in the rear of a vehicle and recognize a dividing line in the captured image, information on a dividing line recognized in the rear of the vehicle has to be corrected to be that at a position of front wheels of the vehicle. To this end, a yaw angle of the vehicle with reference to a lane has to be found precisely as information to be used for the correction.
For instance, Patent Document 1 discloses a device configured to find a road vanishing point that is a point where two parallel road lines cross each other and vanish in an image captured by a vehicle-mounted camera and to calculate an attitude parameter (attitude angle (yaw angle)) of the vehicle-mounted camera on the basis of these two parallel road lines and the road vanishing point.    Patent Document 1: JP Patent Publication (Kokai) No. 07-147000 A (1995)